Correlated excimer formation and molecular rotational dynamics in phenylacetylene dendrimers

Steady-state and time-resolved fluorescence data are used to examine the ph otophysical characteristics of a series of phenylacetylene dendrimers. Corr elated excimer formation is observed in some solvents which is found to dep end strongly upon initial excited-state placement within the dendrimer fram ework. The results suggest two distinct solvated molecular environments whi ch give rise to independent photophysical behaviors. Models of excimer form ation dynamics and relaxation kinetics are described. Additionally, fluores cence anisotropy measurements are examined in the context of simultaneous p robe wobbling-in-a-cone and macromolecular dendrimeric rotation as the mech anisms leading to fluorescence depolarization. Approximate solutions to the model are shown to provide good descriptions of the solvated molecular dyn amics.